Door mechanism for induction heating apparatus



June 12, 1956 c. N. HOWELL 2,750,486

DOOR MEcHANIsM FOR INDUCTION HEATING APPARATUS Filed March I0, 1953CHARLES N. HOWELL 1F-i5 :l BY

ATTORNEY DUR MCHANISM FR INDUCTEON HEATENG AFPARATUS Charles N. Howell,Poland, Ohio, assigner to Lombard Corporation, Youngstown, Ulhio, acorporation of Ohio Application March 10, 1953, Serial No., 341,486

12 Claims. (Cl. 219-1tl.67)

The present invention relates to induction heating apparatus, and moreparticularly to an improved and simpliiied power mechanism for openingand closing the work-retaining door of an inductionV billet heater, forexample.

in the practice of heating cylindrical billets, for eX- ample, byelectric induction processes it is common to provide a relatively heavydoor or other work-retaining means at the open end of the inductioncoils of the heater so that upon application of electric energy to theheater coils the work being heated will not be propelled out of theheater by a so-called motor action which is caused by the creation ofopposing electric elds in the coils and work. Often the propelling forceexerted upon a billet being heated is of considerable magnitude. And,accordingly, the work-retaining door must be relatively strong andarranged to be firmly held in closed position during heating operations.

Thus, it is a primary object of the present invention to provide anautomatic mechanism for opening and closing a work retaining door of aninduction heating device which mechanism is characterized by simplicityof constructon and operation, high strength and positiveness of action.

It has also been proposed to the induction heating art to provideheating apparatus of the type herein contemplated with a suitablecontrol device, such as a thermocouple for example, which device ismounted in the workretaining door of the heating apparatus and thusmaintained in contact with the work to be heated during the entireheating operation. This arrangement is advantageous in that thethermocouple or other device may be utilized to automatically initiateand/or terminate heating operations in accordance with the condition ofthe work.

v Specifically, it has been proposed to resiliently mount a thermocoupledevice in the work-retaining door of an induction billet heater and tocondition energization of the induction coils of the heater upon contactof the thermocouple with the work upon closing of the workretainingdoor. This arrangement insures that the workretaining door will beproperly closed before energization of the coils, and also that thethermocouple will be in proper contact with the Work before a heatingoperation may be initiated so that uniformly accurate control of theheating operation may be provided.

In heater installations where a thermocouple or other control device isprovided in the work-retaining door as set forth above it is necessarythat the door be closed gently so that the control device is not damagedand additionally so that the work is not jarred away from the device.Accordingly, it is another object of the present .2,750,486 PatentedJune 12, 1956 invention to provide an automatic mechanism for closingthe work-retaining door of an induction heating device which, inaddition to having the characteristics of Simplicity and ruggedness, isoperative to ease the workretaining door into fully closed position, andto lock the same in such position, all in accordance with the desiredoperation of the apparatus.

More specifically, it is an object of the invention to provide anautomatic door operating mechanism of the `tye herein contemplated whichmay advantageously utilize a conventional hydraulic cylinder, forexample, as a source of motive power, and in combination therewith asimplified arrangement for eifecting a continuously decelerating closingmovement of the door whereby the same may be eased into closed positionin the manner desired.

A further object or" the invention resides in the provision of anautomatic door operating mechanism as above characterized wherein anoperative component of the mechanism comprises a part or parts of aloading table, conveyor dveice or other service structure for theinduction heating device. A loading table, conveyor device or otherservice structure being commonly employed along with such heatingapparatus, the apparatus or mechanism of the present invention ismaterially simpliiied by the incorporation thereinto of such device orvstructure as will appear.

The above and other objects and advantages of the invention will becomeapparent upon full consideration of the following detailed specificationand accompanying drawing wherein is disclosed a preferred embodiment ofthe invention.

In the drawing:

Figure l is a side elevation of an induction billet heating devicehaving a Work-retaining door and automatic door operating mechanismconstructed in accordance with the teachings of my invention;

Figure 2 is a fragmentary top plan view of the apparatus of Figure l;and

Figure 3 is an enlarged fragmentary view of the induction heating deviceof Figure 1, illustrating details of construction of the work-retainingdoor thereof, including a representative arrangement for mounting athermocouple or other control device therein.

Referring now to the drawing, the numeral 1t) designates, generally, aconventional electric induction heating furnace of a type commonlyemployed for heating cylindrical billets of metal. In accordance withconventional practice the furnace 10 is provided with a horizon-v tallydisposed work receiving coil 11 having a front opening 12 for loadingand unloading billets of material, and having a suitable door 13 forclosing o the opening 12 during heating operations. Suitiable electricalcircuitry, not shown, is also conventionally provided for connecting thework receiving coil 11 to a source of alternating energy as will beunderstood.

Details of construction of a work-retaining door 13 of a preferred typeare shown in Figure 3, and it will be observed therein that the door 13is provided centrally with a recess 14 for receiving and movablymounting a conventional thermocouple device 15. Preferably, thethermocouple device 15 is of a type disclosed in U. S. Patent No.2,466,137, comprising a pair of spaced probes 16 and 17 of dissimilarmetal, which probes are provided with pointed outer end portions andsuitable circuit connections, not shown, leading to a voltage responsivemeter or control device, also not shown. The arrangement is such that inoperation of the thermocouple device the pointed probes 16 and 17penetrate the outer surface of material (a billet 18, for example) underobservation whereupon an electric potential is generated by the probeswhich is in proportion to the temperature of the material. The potentialthus generated may be utilized to energize a temperature-calibratedmeter,y for example, or to perform a control function, or both as thecase may be.

Control arrangements including the above described type of thermocouplehave been found to be particularly desirable in the induction heating ofaluminum workpieces since the probes 16 and 17 are caused to penetratethrough the oxide lilm which is invariably present on the surface ofaluminum material. And the current conductive properties of aluminum aresuch that the material itself comprises an electrical junction for theprobes. More commonly, such junctions are provided by directlyconnecting (by welding or brazing, for example) the dissimilar metals.

In the illustrated arrangement probes 16 and 17 are movably carried inthe door 13 by means of a rod 19 which is slidably received in therecess 14. As contemplated, the structure is such that the pointed outerends of the probes 16 and 17 project somewhat from the inner face of thedoor 13 whereby upon closing of the door against the forward end of abillet 18 the probes 16 and 17 will be brought into resilient butforceful engagement with the end of the billet. Initial penetration ofthe probes through the oxide lm of the material and subsequentmaintenance of proper electrical contact between the probes and thematerial is effected through the use of a suitable spring 20 as will beapparent.

In addition to the use of the particular type of thermocouple devicedescribed above, in the manner above explained, it has been furtherproposed to condition energization of the heating coil 11 upon priorproper contact of the thermocouple with the billet 18. A representativearrangement for accomplishing this mode of operation is also illustratedin Figure 3 and comprises a suitable sensitive switching device 21 whichis mounted on the door 13 adjacent the slidably retained rod 19 mountingthe thermocouple device 15. In the particular embodiment illustrated therod 19 is provided with a suitable cam surface in the form of a notch 22which is adapted to engage an operator 23 for the switch 21 whereby uponmovement of the thermocouple device against the action of spring 20 theswitch 21 will be closed, energizing coil 11, or conditioning it forenergization as the case may be. Thus, it will be understood that properpositioning of the thermocouple device 15 in relation to the billet 18is necessary to condition the apparatus for operation. And this in turnassures that the door 13 will be properly closed prior to energizationof the coil 11 so that it is impossible to propel the billet 18 out ofthe furnace 10 by accidental or inadvertent energization of the coil 11with the door 13 in an open position, for example.

Upon consideration it will be apparent that in order to properly andeffectively operate an induction furnace in which the above describedcontrol instrumentalities are incorporated it is necessary that care beexercised in the closing of the door 13 and that the same be maintainedfirmly closed during heating operations. Thus, it will be readilyunderstood that if the door 13 is closed too rapidly the relativelydelicate components of the thermocouple device may be damaged and/or thebillet 18 may be jarred away from the face of the door in which caseenergization of the furnace is precluded by failure to close switch 21.Accordingly, the present invention is primarily concerned with theprovision of automatic mechanism of a simplied character which isoperative to assure proper closing of the door 13 and subsequentmaintenance of the same in a closed condition throughout the heatingoperation.

Referring particularly to Figures 1 and 2 it will be observed that thedoor 13 is hinged to the main frame of the furnace 10 by means of anelongated arm member 24, which should be of relatively rigidconstruction. The arm 24 is pivotally secured to the furnace 10 at apoint located substantially below the door 13. The construction is suchthat the door 13 may be moved from a closed position, as illustrated, toan open position as indicated in Figure 1 by broken lines.

Positioned opposite the front face of the furnace 10 closely adjacentthereto is a loading table 25, for example, or other service structuresuch as may be conveniently utilized in assisting the loading andremoving of workpieces from the furnace. In accordance with theteachings of the invention the table 25 is of rigid construction,utilizing a plurality of I-beam members 26 and 27 for supporting legs.And further in accordance with the invention the front supporting legsare provided with upper portions 28 which incline upwardly and outwardlyof the table 25 toward the front face of the furnace. Preferably twosuch supporting legs 26 are provided, and as shown in Figure 2 these arepositioned in straddling relation to the arm 24 so that the arm and doorcarried thereby may be pivoted between the legs 26 between open andclosed positions.

Pivotally mounted on the floor or supporting base 29 for the apparatusis a hydraulic cylinder 30, preferably of a double acting type, whichhas an elongated piston rod 31 carrying a plurality of rollers 32 and 33at its upper end. The center roller 33, of the plurality thereof, isadapted to engage the outer face of the arm 24 in the manner shown inFigure l. Likewise, the outer rollers 32 are adapted to engage the outersurfaces of the inclined portions 28 of spaced legs 26. The arrangementis such that as the piston rod 31 is extended from cylinder by suitableapplication of fluid pressure the rollers 32 and 33 will act oppositelyupon the inclined surfaces 28 and arm member 24 whereby to force thedoor 13 into a closed position.

Preferably the upper end portions 34 of the inclined surfaces 28 arevertically disposed and positioned substantially directly opposite thedoor 13 so that outward pressure upon the door while the same is in afully closed position is resisted directly by the rigid frame structureof the table 25 rather than by the cylinder 30.

It should be particularly noted in Figure 1 that when the cylinder 30 isretracted and the door 13 in fully open position roller 33 will act uponarm member 24 at a short distance from its pivotal support, and that thedirection of extending movement of the rod 31 is substantially at rightangles to the arm. Thus, it will be understood that the initial closingmovement of the door 13 will take place at a relatively rapid rate.

However, as the piston rod 31 becomes further extended roller 33 actsupon arm member 24 at a progressively increasing distance from itspivotal support. And, in addition, the component of movement of thepiston rod 31 acts at a progressively decreasing angle to the axis ofthe arm member 24. The combination of these above mentioned effectscauses the closing movement of the door 13 to be rapidly deceleratedfrom its initially fast movement so that a gentle closing movement isobtained which will neither cause damage to the thermocouple device 15nor cause the billet 18 to be jarred away from the face of the door. Andwhen the door 13 is in a fully closed position any opening forcesexerted thereon act directly against the frame structure of the table 25rather than through the cylinder. Thus the cylinder 30 may be of arelatively low power type as will be readily appreciated.

Opening of the door 13 after a heating operation is effected byretracting the piston rod 31, whereupon the door 13 is urged outwardlyof the opening 12 by means of a suitable spring 35, for example. Or insome instances the door 13 and arm 24 may be so arranged that the weightof the door acts to effect opening movement upon retraction of the rod31. A suitable recess 36 is of course provided in the surface of table25 so that the door 13 may be moved to a fully open position as shown inFigure l.

The advantages of the invention should now be readily apparent. Theapparatus is of ultimate simplicity and is easily and inexpensivelyconstructed, yet provides a substantially improved arrangement for thepurpose intended. With a conventional hydraulic actuator and otherelementary components l have been able to effect a door closing movementwhich is rapid during the initial por tion of the movement while beingslow and gentle at the end of the movement. Thus, while the door i3 isslowly eased into closed position to prevent damage to the controldevices carried on the door, the overall time of closing movement ismaintained at a minimum so that rapid production rates may be obtained.

The invention is further advantageous in that the incorporation thereofinto conventional induction heating apparatus requires an absoluteminimum of additional apparatus. And in many instances the loading tableor other service structure utilized in conjunction with the furnace maybe readily modified to provide an inclined cam surface for translatingthe extending movement of cylinder into the desired closing movement ofthe furnace door.

The invention is, of course, not restricted to the specific embodimentthereof herein illustrated. For example, in many instances it may bedesirable to utilize means other than a door, as such, for retaining abillet within the coil 11.

Other possible modifications of the specific apparatus illustratedherein include arrangements wherein the initiating switch is eliminatedand the functions thereof are carried out by suitable control means, notshown, acting in response to an electric circuit being completed uponcontact of the thermocouple probes l5 and i6 with a billet i3. Thus,reference should be had to the following appended claims in determiningthe true scope of the invention.

I claim:

l. In an induction furnace of the type having induction coils and awork-retaining door adjacent said induction coils, and control meanscarried by the door and adapted to have contact with work contained insaid furnace; the combination of means comprising an arm for pivotallymounting said door at a point substantially below said door, said armbeing of relativeily rigid construction and having an outer bearingsurface, a hydraulic cylinder pivotally mounted adjacent said furnaceand below said door, said cylinder having an elongated piston rodcarrying a plurality of rollers at its upper end, one of said rollersbeing adapted to engage said bearing surface, means positioned adjacentsaid cylinder and on the opposite side thereof from said cylindercomprising an inclined bearing surface extending upwardly and inwardlytoward said furnace, others of said plurality of rollers being adaptedto engage said inclined bearing surface, the arrangement being such thatupon extension of said piston rod said rollers move along said firstmentioned and inclined bearing surface to impart an initially rapid butprogressively decelerating closing pivotal movement to said door.

2. Apparatus according to claim l further characterized by said meanscomprising said inclined bearing surface including a bearing portiondisposed in spaced substantially parallel relation to said arm when saiddoor is in fully closed position, the space between said door and saidlast mentioned bearing portion being substantially equal to the diameterof said rollers whereby opening forces against said door are transmitteddirectly through said rollers to said last mentioned bearing portion.

3. Apparatus according to claim l further including a loading table forsaid furnace positioned adjacent the front face thereof, and furthercharacterized by said in- 6 clined bearing surface comprising supportingmeans for said table.

4. In an induction furnace of the type having induction coils and awork-retaining door adjacent said induction coils, and control meanscarried by the door and adapted to have contact with work contained insaid furnace; the combination of means comprising an arm for pivotallymounting said door at a point substantially below said door, said armbeing of relatively rigid construction and having an outer bearingsurface, a hydraulic cylinder pivotally mounted adjacent said furnaceand below said door, said cylinder having an elongated piston rodcarrying a plurality of rollers at its upper end, one of said rollersbeing adapted to engage said bearing surface, means positioned adjacentsaid cylinder and on the opposite side thereof from said furnace forengaging others of said plurality of rollers, said last mentioned meanscomprising a cam surface whereby upon extending movement of said pistonrod said rollers will act upon said cam and bearing surfaces to movesaid door into a closed position.

5. Apparatus according to claim 4 further characterized by said camsurface comprising a portion disposed in spaced substantially parallelrelation to said bearing surface when said door is in a closed positionwhereby opening forces on said door are transmitted directly throughsaid rollers to said cam surface portion.

6. In an induction furnace of the type having induction coils and awork-retaining door adjacent said induction coils; the combination ofmeans comprising an arm for pivotally mounting said door at a pointsubstantially removed therefrom, said arm being of relatively rigidconstruction and having an outer bearing surface, a cam surfacepositioned adjacent said door in spaced relation thereto and comprisinga bearing surface inclined toward said furnace from a point adjacent thepoint of pivotal mounting for said door to a point adjacent said door,means comprising a plurality of rollers and carrier means therefor forcooperatively engaging said bearing surfaces, and means to move saidrollers along said inclined bearing surface.

7. In an induction furnace of the type having induction coils and awork-retaining door adjacent said induction coils; the combination ofdoor operating means comprising an arm for pivotally mounting said Workretaining door at a point substantially removed therefrom, said armbeing of relatively rigid construction and having a bearing surface,means comprising a roller and carrier means therefor for engaging saidbearing surface, means to move said rollers along said bearing surface,and means to confine movement of said rollers to a predetermined pathwhereby said arm is caused to pivot about said mounting to move saiddoor into a closed position.

8. Apparatus according to claim 7 further characterized by said path ofmovement of said rollers when effecting a closing movement of said doorleading progressively away from said pivotal mounting.

9. Apparatus according to claim 7 further characterized by said pathbeing inclined toward said furnace in a direction from the point ofpivotal mounting of said door to a point adjacent said door.

l0. In an induction furnace of the type having induction coils and awork-retaining door adjacent said induction coils; the combination ofmeans for pivotally mounting said work retaining door at a pointsubstantially removed therefrom, door operating means comprising an armrigidly attached to said door, said arm having a bearing surface,follower means adapted to engage said bearing surface, and means to movesaid follower means along a predetermined path leading progressivelyaway from the point of pivotai mounting of said door whereby aninitially rapid but progressively decelerating closing movement may beimparted to said door.

ll. Apparatus according to claim l0 further characterized by said meansto move comprising a hydraulic actuator and means to mount said actuatoradjacent said furnace.

12. Apparatus according to claim 11 further characterized by saidfollower means comprising a roller carried by said actuator, and saidmeans to move said follower means along a predetermined path including acam surface, a service structure for said furnace positioned adjacentthe front face thereof, said cam surface comprising a portion of saidservice structure.

References Cited in the le of this patent UNITED STATES PATENTS HeislerJune 5, 1923 Strickland Aug. 3, 1943 Denneen et al. Sept. 14, 1943Chadwick et al. Oct. 26, 1948 Vollrath Apr. 5, 1949 West June 28, 1949Lackner et al Apr. 20, 1954

